Prevalence of Chlamydia trachomatis in Pregnant Iranian Women: A Systematic Review and Meta-Analysis

Several studies have been conducted regarding the prevalence of Chlamydia trachomatis, Mycoplasma hominis, and Ureaplasma urealyticum in pregnant Iranian women. However, it is necessary to combine the previous results to present a general assessment. We conducted the present study based on systematic review and meta-analysis studies according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). We searched the national and international online databases of MagIran, IranMedex, SID, MedLib, IranDoc, Scopus, PubMed, ISI Web of Knowledge, and Google Scholar search engine for certain MeSH keywords until June 16, 2017. In addition, heterogeneity, sensitivity analysis, subgroup analysis, and publication bias were performed. The data were analyzed using random-effects model and Comprehensive Meta-Analysis version 2 and P value was considered lower than 0.05. The prevalence of Chlamydia trachomatis in 11 surveyed articles that assessed 2864 pregnant Iranian women was 8.74% [95% confidence interval (CI): 5.40-13.84]. The prevalence of Chlamydia trachomatis was estimated 5.73% (95% CI: 2.09-14.73) and 13.55% (95% CI: 11.23-16.25) by enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR), respectively which the difference was not significant (P=0.082). The lowest and highest prevalence of Chlamydia trachomatis was estimated in Tehran province [4.96% (95% CI: 2.45-9.810)] and Ardabil province [28.60% (95% CI: 20.61-38.20)], respectively. This difference was statistically significant (P<0.001). Meta-regression for the prevalence of Chlamydia trachomatis based on year of the studies was significant with increasing slope (P=0.017). According to the systematic review, the prevalence of Mycoplasma hominis and Urea plasma urealyticum indicated 2 to 22.8% (from 4 articles) and 9.1 to 19.8% (from 3 articles), respectively. There was no evidence of publication bias (P value for Begg and Eggers’ tests was 0.161 and 0.173, respectively). The prevalence of Chlamydia trachomatis is high among pregnant Iranian women. Screening pregnant women as part of preventive measures seem necessary considering the potential for maternal and fetal complications.


Introduction
Pregnancy is a serious period in women´s lives, which is related to physiological changes, such as weakening the immune system (1,2). Reproductive tract infections are one of the most serious public health issues in developed and developing countries (3). Chlamydia trachomatis is one of the most common sexually transmitted diseases worldwide (4). Colonization of Chlamydia trachomatis in the reproductive tract of pregnant women causes complications such as infertility, chronic pelvic pain, ectopic pregnancy, premature rupture of membranes (PROM), prematurity, spontaneous abortion, and perinatal mortality (5,6). The prevalence of Chlamydia trachomatis infection is currently increasing throughout the world. The treatment costs of Chlamydia trachomatis infection is estimated to be more than 2 million US dollars. Diagnostic costs are much lower than treatment costs. Therefore, timely diagnosis and screening can decrease the prevalence of reproductive tract infections and reduce treatment costs of this disease (7).
The level of immunity in the body decreases during pregnancy (2). A weak immune system increases the risk factor for the entrance of infectious agents into the vagina. Ureaplasma urealyticum and Mycoplasma hominis are genital mycoplasmas that can be detected in the lower genitourinary tract of sexually active women as a result of colonization of the genital tract through sexual contact (5). These microorganisms can affect each part of the urogenital system and cause infection (8).
These microorganisms have an important role in infections and potential complications during pregnancy. Therefore, it is necessary to be aware of prevalence patterns to plan and screen pregnant women for these microorganisms. Several studies have been conducted in Iran to determine the prevalence of Chlamydia trachomatis, Mycoplasma hominis, and Ureaplasma urealyticum in pregnant Iranian women (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21). Combining the previous results to present a general assessment seems necessary. A review of all relevant documents and presenting a general assessment based on systematic review and meta-analysis studies can provide a more detailed picture of the dimensions of this problem in pregnant women (22)(23)(24). Therefore, we have conducted the present meta-analysis women from Iran.

Study protocol
We conducted the present study based on systematic review and meta-analysis studies according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (24). To avoid bias, two researchers conducted independent searches, selection of studies, quality assessment, and data extraction. In case of dispute, the case was referred to a third researcher. The final agreement was reached as a general discussion.

Search strategy
We searched national online databases such as MagIran, IranMedex, SID, MedLib, and IranDoc, in addition to the international databases Scopus, PubMed, ISI Web of Knowledge, and Google Scholar search engine till June 16, 2017. To maximize the comprehensiveness of the search, we used MeSH keywords with all possible combinations with "OR" and "AND" in the English databases: 'Epidemiology', 'Prevalence', 'Chlamydia', 'Ureaplasma', 'Mycoplasma', 'Sexually transmitted diseases', 'Reproductive tract infections', 'Pregnant women', 'Pregnancy', 'Gestational', and 'Iran'. At the end of the search, the titles of the collected articles were entered into EndNote™ software to find similar articles.

The studied population
The studied population included pregnant Iranian women. The positive result for Chlamydia trachomatis was determined by enzyme-linked immunosorbent assay (ELISA) or polymerase chain reaction (PCR). The positive results for Mycoplasma hominis and Ureaplasma urealyticum were determined by PCR (25,26).

Inclusion and exclusion criteria
Inclusion criteria of this study consisted of a reference to the prevalence of Chlamydia trachomatis, Mycoplasma hominis, and Ureaplasma urealyticum in pregnant Iranian women, either in Persian or English. Exclusion criteria were: non-random sample size; irrelevance; limited information such as failure to report disease prevalence; review articles, case reports, and editorials; duplicate articles; and failure to diagnose based on laboratory results.

Quality assessment
In the next step, researchers assessed the quality of articles according to the modified Newcastle Ottawa Scale (NOS) for cross-sectional studies (27) that consisted of 8 sections in 4 categories, including selection, comparability, exposure assessment, and outcome. This scale ranges from 0 to 9 point. The minimum acceptable score was 7.

Data extraction
All included articles were prepared for data extraction by a pre-prepared checklist. The checklist included the author's name, year of the study, the location of the study, study design, sample volume, mean age, quality score and the prevalence of Chlamydia trachomatis, Mycoplasma hominis, and Ureaplasma urealyticum.

Statistical analysis
The variance of each study was estimated according to the binomial distribution. We used the Q test and I 2 index to assess the heterogeneity of the studies (28). Studies with heterogeneity greater than 75% fell into the category of high heterogeneity. If the I 2 index was lower than 25%, the heterogeneity was low; between 25-75% indicated medium heterogeneity, and higher than 75% indicated high heterogeneity. Due to the significance of the I 2 index, we used the random effects model for the meta-analysis (29,30). Sensitivity analysis was conducted by deleting every single study from meta-analysis. Subgroup analysis based on province, diagnostic test, year of studies and meta-regression based on years and diagnostic test were used to detect heterogeneity of papers with the subject of Chlamydia trachomatis. Egger and Beggs' tests were used to assess publication bias. The data were analyzed using Comprehensive Meta-Analysis (CMA) version 2. P values were considered less than 0.05.

Prevalence of Chlamydia trachomatis
We assessed 11 surveyed articles that had a sample size of 2864 pregnant Iranian women and determined the prevalence to be 8.74% (95% CI: 5.40-13.84), and high heterogeneity was estimated between studies (P<0.001, I 2 = 92.32%) for Chlamydia trachomatis (Fig.2A). The lowest prevalence pertained to the study by Khezerdoust et al. (11) in Tehran (2.2%), whereas the highest prevalence was reported by Rohi et al. (16) in Ardebil (28.6%). Sensitivity analysis indicated that the pooled results were robust (Fig.2B).

Publication bias
Funnel plot for the prevalence of Chlamydia trachomatis did not reveal significant publication bias (P value for Begg and Eggers' tests was 0.161 and 0.173, respectively) (Fig.4).

Discussion
Awareness of the prevalence pattern and screening for diseases that affect the health of the mother and fetus is necessary during pregnancy. The present study is the first systematic review to assess the prevalence of Chlamydia trachomatis, Mycoplasma hominis, and Ureaplasma urealyticum in pregnant Iranian women.
We have determined the prevalence of Chlamydia trachomatis in 11 surveyed articles that had a sample size of 2864 pregnant Iranian women to be 8.74% (95% CI: 5.40-13.84). The prevalence of this disease is 10.1% in China (31), 10.5% in Saudi Arabia (32), and 35% in India  Azami et al.

Logit event rate
Int J Fertil Steril, Vol 12, No 3, Oct-Dec 2018 197 (33). However, the results of the present study are similar to those reported in Scotland (34).
The prevalence of Chlamydia trachomatis in some studies was higher than the present study (35,36). On the other hand, the results of other studies were in the same range as the present study (37,38), though not exactly identical. Inconsistent results with the present study might be due to cultural differences, social and religious norms, and mean age of the studied populations. The high prevalence of this infection in women age 20 and above might be due to early onset of sexual intercourse, numerous pregnancies, and the use of oral contraceptives (39,40). Women with vaginal secretions and inflammatory changes in cervical cytology are more prone to infection and should be examined by their gynecologists (41). Several documents have demonstrated that dysuria, vaginal discharge, and lower abdominal pain may be clinical symptoms of this infection (41,42), which are more common in pregnant women.
Age (particularly 18-27 years) and socioeconomic conditions such as an urban residence or low income (43) are among the risk factors for Chlamydia trachomatis in pregnant women. A study in Japan has reported a significantly high prevalence of Chlamydia trachomatis in primiparous pregnant women (44).
Recent studies report a significant relationship between Chlamydia trachomatis infection to preterm delivery (5,45). The importance of Chlamydia trachomatis for midwives is due to the ability of this microorganism to cause urethritis, cervicitis, preterm births, PROM, and neonatal infections as the baby passes through the birth canal, in addition to abortion, maternal mortality, and stillbirth. Repeated screening tests in the first prenatal examination and during the third trimester of pregnancy, along with successful treatment with erythromycin can reduce the complications of pregnancy according to the American College of Obstetricians and Gynecologists (5,6,45,46). These bacteria can be easily detected by cell culture and serological methods that use micro-immunofluorescence techniques, ELISA, the complement fixation test (CFT), antigen detection methods, molecular methods (DNA hybridization, nucleic acid amplification techniques), and direct cytological methods (Giemsa, Gimenez, and hematoxylin stains) (25,26). The best and most cost-effective method to determine whether the infection during pregnancy is acute or chronic the ELISA test (47,48). In the present study, we have noted that the prevalence of Chlamydia trachomatis according to PCR results was not significantly more than ELISA (P=0.082).
The prevalence of Mycoplasma hominis in pregnant Iranian women from 4 studies was 2 to 22.8% (17)(18)(19)(20). The prevalence of Ureaplasma urealyticum in Iranian pregnant women was 9.1 to 19.8% (16)(17)(18). Meta-analysis was not performed on the prevalence of Mycoplasma hominis and Ureaplasma urealyticum because of a scanty number of studies. Therefore, we recommend conducting more research in this area for future studies. Mycoplasma hominis had the following prevalence in other countries: 3.7% (Poland), 31.5% (Portugal), 11.2% (Japan). Ureaplasma urealyticum had the following prevalence in other countries: 29.8% (Poland), 27.8% (Portugal), and 8.7% (Japan) (49)(50)(51). These results did not agree with the present study, which might be due to cultural differences, social and religious norms, and the mean age of the studied populations.
Mycoplasma hominis is isolated from the vaginal secretions of 15-70% of women. Ureaplasma urealyticumis is isolated from the vaginal secretions of 40-95% of women (8,(52)(53)(54)(55)(56). Mycoplasma hominis and Ureaplasma urealyticumis are transferred to the fetus during pregnancy or normal vaginal delivery. They are often associated with cervicitis, vaginitis, pyelonephritis, pelvic inflammatory disease, postpartum septicemia, uterine infections, meningitis, PROM, postpartum fever, preterm delivery, and low weight premature birth (8,57,58). Most premature births for women with these two infections happen before the 34th week of pregnancy (59,60). However, no significant relationship has been found between these infections and adverse effects on pregnancy in some studies (51). Studies conducted on Mycoplasma hominis have demonstrated that it caused adnexal lesions but not salpingitis (53). Ureaplasma urealyticum is the main cause of non chlamydial and nongonococcal urethritis, chorioamnionitis, cervicitis, vaginitis, sepsis and preterm delivery. Moreover, it may cause pneumonia, meningitis and even death of the infant as the baby passes through the birth canal (56). The role of Ureaplasma urealyticum has not been specified (54). PCR is often used to diagnose this infection in Iran. However, the molecular technique has also been used in some studies in Iran (61). Therefore, considering the fact that failure to diagnose, prevent, and treat these infections leads to dangerous complications, it is necessary to identify these bacteria, particularly in pregnant women (53,62).
Factors that increase the prevalence of prenatal infections in women include young age (adolescents and young adults); use of an intrauterine device (IUD); low level of education, unemployment, and low income; multiple sex partners; not using a condom, diaphragm or spermicide; lack of attention to individual health care for both men; and women and smoking, alcohol consumption, and drugs (25,63,64).
Several meta-analysis studies in Iran have focused on other infections in pregnant women and reported the following results: prevalence of urinary tract infection (11.2%) (65), hepatitis B (2%) (66,67), and Helicobacter pylori (45.9%) (68,69). According to Ahmadi et al. (70), the prevalence of urogenital mycoplasmas in the male population was 11.1% (95% CI: 7.4-16.4) and 12.8% (95% CI: 9.8-16.5) in females, which was high. Hence, Chlamydia trachomatis is one of the most common infections in pregnant Iranian women. Determining the causes of these infections and methods of prevention should be among the medical priorities for pregnant Iranian women to ensure the health of the next generation.
The limitations of the study included the failure to search using a combination of words in internal databases due to low sensitivity and the inability to perform further subgroup analysis because of the limited number of studies.
Future case-control studies to determine the role of various risk factors in Iranian societies seems necessary.

Conclusion
The high prevalence of reproductive tract infections among pregnant Iranian women necessitates screening these women as a preventive measure. Therefore, timely recognition and treatment of this disease can prevent maternal and fetal complications.